1. Field of the Invention
The present invention relates to an electron gun used with a cathode ray tube, and more particularly, to an electron gun used with a multi-media monitor with an improved triode.
2. Description of the Related Art
Color cathode ray tubes (CRTs) are classified into a color picture tube (CPT) to display a moving picture as in a television, or in connection with a video and a color data tube (CDT) to display text information. CPTs need a high-brightness and low-resolution whereas CDTs need a low-brightness and high-resolution.
Combined with the recent tendency for high-brightness monitors, the popularization of asymmetric digital subscriber lines (ADSLs) or cable TVs has added a television tuner or video capture function to personal computers (PCs). Accordingly, computers capable of receiving and recording TV broadcasts have been commercialized as diversified products. Such a computer monitor needs a multi-media CRT capable of simultaneously displaying still and moving pictures and text information.
To display a high-resolution output with a color CRT for a computer monitor, a high-frequency signal is used, compared to a CPT for a moving picture display. Due to difficulty applying a high drive voltage, such a high-frequency signal is generated with the application of a low drive voltage. As a result of the application of the low drive voltage, working current and brightness or luminance are reduced.
To realize a high-brightness CRT, a method of increasing a cathode current level, a method of improving electron beam utilization efficiency, or a method of improving phosphor screen luminance efficiency has been suggested. The method of increasing the cathode current level needs a high cathode drive voltage for a greater beam current. However, the application of a high cathode drive voltage to an electron gun generates saturation current due to signal trailing or spreading, thereby resulting in divergence of an electron beam.
To address these drawbacks, there is a need to design a chassis circuit having stable amplification characteristics by using reliable, high-capacity circuit parts. However, this circuit construction adds an extra cost.
As a method of increasing current density while reducing the cost of the circuit implementation, a method of reducing a cathode spot cutoff voltage during the operation of a CRT has been suggested. When the cathode spot cutoff voltage is lowered during the CRT operation, a high current response is ensured even with a low drive voltage. However, a beam loading area on the cathode and the beam size are adversely increased even in a low-current CDT mode, thereby lowering resolution.
To solve the problem of such a resolution reduction, a method of reducing the diameter of an electron beam aperture of a control electrode, which is adjacent to the cathode of the electron gun, to reduce the cross-over diameter of an electron beam in the triode and further to reduce aberration caused by a pre-focusing lens formed in the triode, has been suggested. The beam size can be reduced with this method. However, the diameter of the control electrode is substantially too small to assemble an electron gun.
To eliminate the above problems, an example of a conventional electron gun is disclosed in Japanese Laid-open Patent publication No. 1999-224618. The electron gun includes first, second, and third electrodes sequentially arranged further from the cathode and a modulation electrode between the second and third electrodes.
As another example, an electron gun with enhanced focusing characteristics at a high brightness is disclosed in U.S. Pat. No. 5,689,158, wherein a plurality of electron beam apertures are formed in both control and screen electrodes. Since each of the control and screen electrodes includes the plurality of electron beam apertures, it is difficult to assemble the electron gun. Also, an increased number of electrodes to be controlled is impractical for applications.
Korean Laid-open Utility Model Publication No.1999-033989 discloses an electron gun including three cathodes, a heater for the cathodes, and six electrodes for accelerating electrons generated from the cathodes to focus an electron beam. In the electron gun, a second electrode among the six electrodes for accelerating electrons has an insulator of a predetermined thickness on its one side and an electrode portion of a predetermined thickness on the outer side of the insulator, and a second electrode voltage is applied to the electrode portion.
Korean Laid-open Utility Model Publication No.1999-008925 discloses an example of an electron gun for a multi-media monitor. The electron gun focuses electrons emitted from several cathodes on a screen through a first electrode unit, a second electrode unit, and a main lens unit. The first electrode unit includes two electrodes and a fixing spacer between the electrodes, wherein the fixing spacer has an electron beam aperture at its center.